Friday, July 13, 2012

Neuronal repair and evolution

When it comes to neuronal repair, the actual reason that we can't do it in the CNS is a lot more complicated than the article led you all to believe.Here's the original segment, containing a lot more of the science and a joke about driving the wrong way on an on ramp, inspired by a depressingly true story.

Most neural growth occurs in the axon, the signal
transmitting part of the neuron. During
fetal development, axons need to navigate without the benefit of GPS, mostly
because the average uterus only gets one bar of service. (Or serviced by one
bar. Whichever.) Luckily, axons are tiny frat boys: they can be attracted or
repelled by chemicals called chemotrophic
factors, eventually stumbling their way home to pass out on their
molecular sofas. Once in place, the axons
are surrounded by support cells called glia and the whole thing is
shipped out without any quality control whatsoever.

This sort of precise neural direction is required during
development. Screw up any step and you'll end up with some variety of
catastrophic neurological failure ranging from inability to feel painto being born with only one eye There
are billions of neurons and they all need to get to where they're going and
goddamn stay put. And this is where the glia work their dark magic.

Those glia are the In
a healthy person,that keeps the axon from wandering. But after a spinal cord injury, the growing axon is doing the equivalent of backing down the off ramp because it took the wrong exit. The glia stop all growth while the axon frantically tries to
explain that it's late for a synapse in the knee.